Testing apparatus for measuring transformers



March 10, 1931. e. KEINATH ET AL 1,795,607

TESTING APPARATUS FOR MEASURING TRANSFORMERS Filed March 29, 1929 sSheets-Shet 1 BY fii/Q 744mm March 10; 1931. .G. KEINATH ET AL 1,795,607

TESTING APPARATUS FOR MEASURING TRANSFORMERS Filed March 29, 1929 5Sheets-Sheet 2 I/Vtfe/V'TORS GEORG- KEm/ATH OTTO S E-BER ATTORNEYS.

March 10, 1931. a. KEINATH ETAL 1,795,607

TESTING APPARATUS FOR MEASURING TRANSFORMERS File d March 29, 1929 sSheets-Sheet .3

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I YEA/TO I? s AT'ronn efs Patented Mar. TO, 1931 UNITED- STATES PATENTOFFICE GEORG KEINATH, or nnnmN-cnAnLorrENnURe, AND or'ro' srAnnAu,GERMANY, ASSIGNORS TO srnmnns & nALsxE,

smrnn, or unarm- AKTIENGESELLSCHAFT,

e OF SIEMENS STADT, NEAR BERLIN, GERMANY, A CORPORATION 015 GERMANY ofmeasuring transformers,

rnsrme APPARATUS FOR MEASURING rizANsronMERs Application filed March 29,iezaserial m.

Our present invention relates to the testing and has for its object toprovide means which will o erate accurately and reliably even when weacurrents are employed.

For a thorough explanation of this invention, reference is to be had tothe accompanying drawings, in which Fig. 1 is a diagram of a measuringcircuit such as used prior to our invention, and Fig. 2 is a diagramillustrating certain properties of' the currents existing in thearrangement of Fig. 1; Figs.

3; 4, and 5 are circuit diagrams showing three satisfactory arrangementsembodying the novel features of our resent invention. The measurement 0weak alternating currents by means of their rectification, which is mostsimply done by half periodic interruptions and their measurement then bydirect current instruments, is known. This method is also applicable forthe testing of current transformers in the circuit according to'Figure'l. In this a: indicates the transformer to be tested, a a normaltransformer of the same kind serving as a standard of comparison. Theprimary windings p have thesame current '5 flowing through them. Thesecondary windings 8, ,8: are connected to a resistance B, through whichthe difference of the secondary currents A '5 flows. This differenceaccording to Figure 2 may be resolved into a component f, which is in.

. phase with the secondary current of the normal transformer i and acomponent 8 which is displaced by 90 relatively to the phase of thecurrent i The component 7'' gives the difference of the transformingratios of the two transformers, the component 8 the difference of thephase error. The'two currents f means of a watt meter instrument, ofwhich one coil carries the current A 2' while the other carries acurrent either in phase with i or a current w 'ch is displaced by 90relativel to i If in this measurement it is desire to transform thealternating current by means of half periodic interruptions. intodirect'cur- 1 rent, the two components 7 and 8 may be obtained by thecurrent 2' being sent into the rectifier and the phase of theinterruption so to the friction of the -not be complied with;

850,877, and in Germany January 5 1928.

character as well as special difficulties ap--- pertaining to the methodof connection mentioned-above.

The commutators used in general for the rectifier have the disadvantage,that owing.- brushes, thermal forces are produced which affect verysensitive direct current instruments such as are here mostly used, andfurthermore, the phase can not be very accurately adjusted on theseinstruments. The first defect is overcome according to the presentinvention by usingas a rectifier a frictionless instrument, viz :adiaphragm rectifier. This instrument is similar to a telephone. Thevibrating diaphragm makes contact for half a cycle or wave with a pencilopposite its centre, when the coils are supplied with alternatingcurrent, and an alternating current which is led through this contact isthen interrupted. at each half cycle and thenqaccording to thephaseposition, more or less completely rectified. The-second fault of aninexact phase adjustment is overcome" bythe use of a phase displacen;

There is however something more important than the said faults connectedwith the use of the rectified alternating currents, due directly to themethod of connection shown in Figure 1 of the accompanying drawings. hemeasurement is the-more exact the smaller is the resistance R. If now itwere desired to put a sensitive direct current instrument in the branchwith a rectifier "connected therein, the requirement of a smallresistance could as naturally the current-sensitive instrument has ahigh resistance. This arrangement will also give rise to. the followingconditions: With the making and breaking of the alternating current inany desired phases displaced from each other by a half period, or halfcycle, switching processes take place which lead to a confusion of thecurrent curve to be again These switching operations can also be neg-.lected if the phase displacement in the direct given out.

lie

current instrument to be connected up is very small. This would againnecessitate a greater resistance of the measuring instruments, which isin 0'' position to the requirements of the connection of the resistanceR in the branch. A still worse result of the arrangement of theinterrupter in the branch of R is, however, that on interrupting thisbranch the equalization of the currents in' the branch formed by thesecondary windings s 8 alone would have to take place at once. By thishalf periodic switching over, switching operations are produced in thehighly inductive current circuit of the secondary windings, which makethe whole of the measurement illusory.

According to the present invention the difficulties arising in theconnection according to Figure l are overcome by the measuringinstrument with the rectifier not bein connected in series with theresistance but parallel thereto. The branch with the resistance R istherefore never interrupted and the flow of the current in the secondarywindings is normal. The measuring instrument itself can have a highresistance, as is necessary in order that its indications may not beinfluenced by the switching operation and as is of course proper for aninstrument of high sensitiveness. The current in the measuringinstrument is thus so small compared with the current in the resistanceR, that the influence of its interruptions on the whole circuit may beneglected.

Figures 3, 4 and 5 show circuits according to the invention. In thesethree figures, 'n

(or at) designates the normal transformer used as a standard ofcomparison, and a: (or a) the transformer to be tested. In Fig. 3, S andS are the secondaries of the respective transformers. R is a resistance,A an ammeter, 1' a resistance in series with the secondary oi' thenormal transformer n. From the terminal 1 of the resistance R a line 2runs to the double pole change-over switch 3. In the dotted position ofthis switch the line 2 runs to a diaphragm rectifier 4, from this to themeasuring instrument mV, then through a variable series resistance 5,the second pole of the switch 3 and line 6 to the other terminal 7 ofthe resistance R. The. die hragm rectifier 4 is energized by the coil 8w ich is connected to a phase displacer 9. In order to brin theinterruptor, which is adjusted for a hal period interruption, to such aphase that the half period given by it is in phase with the current ithe switch 3 is set in the position shown in full lines, when the branchwith the rectifier 4 and the indicating instrument 'mV is placed inparallel to a resistance 1- in the secondary circuit of the normaltransformer n. On the adjustment of the phase displacer to the maximumswing of the indicating instrument mV like phase 1s obtained between theenergizing cur- 1 teaser rent of the coil 8 and the secondary current '5On account, however, of the greater sensitiveness .it is preferable toso adjust the phase displacer, that the indicating instrument points tozero, when the two currents mentioned differ by 90 and in order to makethe phases agree, the phase displacer is rotated by 90. If theenergizing current of the coil 8 has been adjusted to a like phase withthe secondary current i instrument gives a throw proportional to thecurrent difference f (Figure 2). If the energizing current in the coil 8is adjusted to a phase difi'erence of 90 with respect to the secondarycurrent 5 then the throw of the indicating instrument is proportional.to the phase error 8, Fi ure 2.

By altering the series resistance 5 of the indicating instrument tocorrespond to different loads, the same throw of the indicatinginstrument can be obtained for the same percentage amount of thecurrentdifierence f or the same angular amount of the phase error t'withall loads. The regulating resistances for the secondary coils s of thetest transformer are shown at 10. A currentindicator A is provided forthis. This is only to indicate whether the secondary windings areconnected aiding each other or opposed to each other. If connectedwrongly the instrument will be deflected and thus give a warning beforeconnecting up the measuring instrument which would be damaged in thecase of a faulty connection.

If it is desiredto obtain a, simultaneous reading of the differences ofthe transmission ratios and of the phase, then two indicatinginstruments are employed in to the circuit as shown in Figure 4. Theinstrument which shows the transmission difference can then becalibrated directly in percentage, if suitable series resistances 5 areprovided for the various loads; the other instrument showing the phasedifference, with the series resistances 5., indicates in a correspondingmanner in minutes. In order, with the same phase displacer, to producetwo energizing currents displaced by 90 in the rectifiers 4 and 4' ofthe two indicating instruments, a phase displacer 9' is preferably used,the Winding of which is connected in three phase star as shown in Figure4. One phase is then taken from a neutral point potential and the otherfrom a linked potential. This connection arrangement is suitable for useby inexperienced attendants. It is also suitable for the testing oftransformers in the working position, also for use when travelling, asthe most sensitive part of-the galvanometer may always be constructed asan indicating instrument with axial bearing.

In the same way as for the testing of a current transformer the testingof a potential transformer may be carried out by comparing with a normaltransformer with the aid of then the indicating Any calculation of theerrors given by the P j indicating instrument which in the first placesistances 15.

diaphragm rectifiers and direct current indieating instruments, as shownin Figure 5. The potential transformers n, m are connected with opposingsecondaries and the potential difference is taken off at switch 13 towhich is connected the indicating instru- -ments for percentage andminutes with the series rectifiers 14 and 14' and the series re- Thephase displacer is connected as in Figure 4:. The use of the saidswitching arrangement may be still further simplified bythe use of anormal transformer having a negligible amount of error:

is only measured as relative to the normal transformer, to bring it toan absolute value,

is then dispensedwith. For example the ac-' curacy of measurement willvery often satis-.

fy practical requirements, if the indications are used withoutcorrection, with an error of the normal transformer of 0.2% in thetransmission ratio and 5-minutes in the phase.

Having now particularly described and as--' certained the nature of oursaid invention and in what manner the same is to 'be per-- formed, wedeclare that what we claim is 1. In a testing arrangement for measuringtransfor mers, a source of alternating electric current, a normaltransformer servingas a standard of comparison, a transformer to betested, the primaries of both transformers receiving current from saidsource, a rectlfierenergized synchronously with sald source and acontact made by said rectifier during alternate half cycles, a directcurrent meter in series with said. rectifier contact, and means forconnecting thesecondaries of said transformers with each other and withthe series connection of the rectifier'contact and the said meter insuch a manner that such meter will permit of measurin the difference ofan electrical characteristic 0 the two transformer secondarieswithrespect to value and phase.

2. In a testing arrangement for measuring transformers, a source ofalternating electric current, a normal transformer serving as a standardof comparison, a transformer to be ,tested, the primaries of bothtransformers receiving current from said source, a rectifier energizedsynchronously with said source and a contact madeby said rectifierduring alternate half cycles, a direct current meter in series with saidrectifier contact, a resistance, .means for connecting said resistancewith the secondaries of said 'transformersin such a.

manner that'the difference between the secondary currents will flowthrough said resistance, means .for arbitrarily adjusting the phase ofthe currentfenergizing the rectifier, a resistance in series with thesecondary of ..the11,Q1lI al transformer, and a' change-over switchwhich the series connection of rectifier contact and direct currentmeter cjn be connected selectively in parallel with one or the other ofsaid resistances.

'3. A testing arrangement accordin to claim 2, in which the secondarycircu1t of the transformer to be tested contains a' variable loadingresistance.

4. A testing arrangement according to transformers receiving currentfrom said source two rectifiers energized synchronously with saidsource, each rectifier having associated therewith, a contact made bythe respective rectifier during; alternate half cycles, two directcurrent meters, each in series with the respective rectifier contact, aresistance, means for connecting said 'resistance with the secondariesof said transformers in such a manner that the difference between thesecondary currents will flow through said resistance, means for arbitrarily adjusting thefi iphase of the current energizing the recti rs, aresistance in serles w1th the secondary of the normal transformer, and a.changerover switch by which the series connections of the rectifiercontacts with the respective direct current meters can be connectedselectively in parallel with one or the other. of said resistances.

7. A testing arrangement according to claim 6, in which thesecondary-circuit of the transformer to be tested contains a variableloading resistance;

-8. A testin arrangement according to claim 6, inclu ing a variableresistance connected in series with each of the respective directcurrent meters.

9. A testin arrangement, accordin to claim 6, in w ich the secondarycircult of the transformer to be tested contains a variable loadingresistance, and in which there are variable resistances, each connectedin serieswith the respective direct currentmeter.

' 10. In a testing arrangement for measuring transformers, a source. ofalternating electrlc' current, a normal transformer serv-' ing as astandard of comparison,'a transformer to be tested, the primaries ofboth transformers receiving current from said source, a rectifierenergized synchronously with said source and a contact made by saidrectifier during alternate half cycles, means 4= meaeo'z' forarbitrarily adjusting the phase of the current energlzing the rectifier,a resistance located in the secondary circuit of the normal transformer,and a change-over switch by which the series connection of rectifiercontact and direct current meter can be connected selectively inparallel with said re-' sistance or with the free ends of the oppositelyseries-connected secondaries of the m transformers.

11. A testing arrangement according to claim 10, in which a variableloading resist-V ance is located in the secondary circuit of thetransformer to be tested.

I 12. A. testin arrangement according to claim 10, in whichavariahleresistance is connected in series with the direct current meter.

13. A testing arrangement according to 29 claim 10, in which a variableloading resistance is located in the secondar circuit of the transformerto be tested, an in which a variable resistance is connected in serieswith the direct current meter.

14. In a testing arrangement for measuring transformers, a source ofalternating electric current, a normal transformer serving as a standardof comparison, a transformer to be tested, the primaries of both antransformers receiving current from said source, two rectifiersenergized synchronously with said source, each rectifier havingassociated therewith, a contact made by the respective rectifier duringalternate half cycles, two direct current meters, each in series with.the respective rectifier contact means for arbitrarily adjusting thephase 0 the current energizing the rectifier-s, a resistance in thesecondary circuit of the normal 40 transformer, and a change-over switchby which the series connections of the rectifier contacts with therespective direct current meters can be selectively either connectedinparallel with said resistance or connected with the free endsof theoppositely seriesconnected secondaries of the transformers;

15. A testing arrangement according to] 7 claim 14, in which a variableloading resistance is located in the secondary circuit of 5c thetransformer to be tested.

16. Ktesting arrangement according to claim 14, in a variable resistanceis connected in series with each of the respective direct currentmeters.

17. A testing arrangement according to claim 14, in which a variableloading resistance is located in the secondary circuit of thetransformer to be tested, and in which ,there are additional variableresistances, so each connected in series with the respective directcurrent meter.

' In testimony whereof we aflix our signa- 1' tures;

- GEORG KEINATH. 65 g OTTO SIEBER.

